Guide to how Theresa May will get her general election on June 8

For months Theresa May and her team have played down the prospect of an early general election.

"It isn’t going to happen. There is not going to be a general election,” the prime minister’s spokesman told lobby journalists last month.

Explaining her change of heart on an early election today, May said: "I have concluded the only way to guarantee certainty and security for years ahead is to hold this election."

So how can she call an early election under the Fixed-term Parliaments Act? And what are the key dates?

All is explained in four simple steps…

STEP 1: THE ANNOUNCEMENT

Under the Fixed-term Parliaments Act 2011, the next general election was not due until 2020. But the prime minister has said she wants to go to the country on Thursday June 8.

May told the Queen of her plans in a phone conversation on Bank Holiday Monday. This morning, she chaired a cabinet meeting in which the date was agreed. She then made the shock announcement on the steps of Downing Street.

STEP 2: THE VOTE

Under the Fixed Term Parliament Act 2011, an early election is possible if there is a motion of no-confidence in the current government. Or if two thirds of MPs back a government motion in the House of Commons calling for an early election.

May has called on the Commons to vote for the early election on Wednesday 19 April.

With 650 MPs in the Commons, Number 10 said this morning that this means 434 MPs must support the government’s motion. The Conservatives have 330 MPs, so May will need the support of at least 104 MPs from opposition parties.

This should be easily achievable now that Jeremy Corbyn has said he is in favour of an early election. The Labour leader said: "I welcome the prime minister’s decision to give the British people the chance to vote for a government that will put the interests of the majority first." The Labour party has 229 MPs.

STEP 3: THE CAMPAIGN

The Queen no longer has the power to dissolve Parliament. This is now scheduled by the Fixed Term Parliament Act to automatically happen 25 days before the election date.

An election on June 8 would therefore mean that parliament would be dissolved on Wednesday 3 May and MPs will be free to pound the pavements up and down the land from then.

Commons leader David Lidington has confirmed this will have to take place just after midnight on 3 May. So in practice it will take place on the night of Tuesday 2 May, he said in the Commons today.

STEP 4: THE CANDIDATES

However we may not know all of the general election candidates until a week later.

One MP who will not be standing again is the arch-Jeremy Corbyn critic Tom Blenkinsop. Moments after the prime minister's announcement, the MP for Middlesbrough South and East Cleveland released a statement on his website saying he would not be seeking re-election.

Alan Johnson has also announced his decision to retire, saying: "For me the personal decision is whether to retire now or in 2022 when I’ll be into my 70s."

Wednesday 10 May is the date when it should be clear exactly who will try to step into the shoes of all departing MPs.

Under Electoral Commission rules, nominations have to be filed by 4pm on the 19th working day before the poll – which is 10 May in this case..

However in practice parties are likely to have candidates in place at least a week beforehand, to allow for paperwork to be filed and all of the necessary arrangements to be made.